This invention relates to actuators. An “actuator” is defined in the Merriam-Webster's Collegiate Dictionary, Tenth Edition as a mechanical device for moving or controlling something. Actuators perform a myriad of functions and enable many modern conveniences.
Various mobile platforms, e.g. aircraft, buses, trains, ships and various other vehicles, use actuators to perform many functions during operation of the mobile platform. For example, aircraft utilize actuators to control the movement of flaps, spoilers and ailerons in each wing during operation of the aircraft. Actuators in the tail of an aircraft control the rudder and elevators, while actuators in the fuselage open and close the doors that cover the landing gear bays. Additionally, actuators are utilized to raise and lower the landing gear of the aircraft and actuators on each engine control thrust reversers by which the plane is decelerated.
In addition to uses in mobile platforms, such as aircraft, actuators are used in computer disk drives to control the location of the read/write head on which data is stored and read from the disk. Actuators are used in robots, i.e., in automated factories to assemble products. Actuators operate brakes on vehicles; open and close doors; raise and lower railroad gates and perform numerous other tasks of everyday life.
Prior art actuators fall into two general categories: hydraulic and electric, with the difference between the two categories being the motive force by which movement or control is accomplished. Hydraulic actuators require a pressurized, incompressible working fluid, usually oil. Electric actuators use an electric motor, the shaft rotation of which is used to generate a linear displacement using some type of transmission.
A drawback with hydraulic actuators is the plumbing required to distribute and control the pressurized working fluid. For example, in an aircraft, a pump that generates high-pressure working fluid and the plumbing required to route the working fluid add weight and increase design complexity because the hydraulic lines must be carefully routed.
Electric actuators, which are powered and controlled by electric energy, require only wires to operate and control but a drawback with prior art electrical actuators can be their reliability. Windings of electrical motors are susceptible to damage from heat and water. Bearings on motor shafts wear out. The transmission between the motor and the load, and which is inherently more complex than the piston and cylinder used in a hydraulic actuator, is also susceptible to wear and tear, and eventually to failure. While electrical actuators have advantages over hydraulic actuators, an electrically-powered actuator that provides increased reliability, would be a significant improvement over the prior art. Fault-tolerance, i.e., the ability to sustain one or more component failures or faults and remain operational, would also provide an improvement over prior art electrical actuators.